AQA GCSE FOUNDATION Chemistry: Endothermic Reactions

AQA GCSE Foundation Chemistry: Endothermic Reactions

Introduction

Endothermic reactions are chemical reactions that absorb energy from their surroundings, causing a decrease in temperature. Think of it like a sponge absorbing water. Just as a sponge becomes heavier when it absorbs water, a reaction mixture becomes colder when it absorbs energy.

Key Concepts

• Energy Transfer: Endothermic reactions require energy to occur. This energy is usually absorbed from the surroundings, causing the temperature of the reaction mixture to drop.
• Enthalpy Change: The enthalpy change (?H) for an endothermic reaction is positive. This indicates that the products have higher energy than the reactants.
• Breaking and Making Bonds: Chemical reactions involve breaking existing bonds and forming new ones. Breaking bonds requires energy, while forming bonds releases energy. In endothermic reactions, more energy is required to break bonds than is released by forming bonds.

Examples

1. Dissolving Ammonium Nitrate: When ammonium nitrate (NH4NO3) dissolves in water, it absorbs heat from the surrounding water, causing the water temperature to decrease. This is why cold packs used for injuries contain ammonium nitrate.

2. Photosynthesis: Plants use sunlight to convert carbon dioxide and water into glucose and oxygen. This process is endothermic, as it absorbs energy from sunlight.

3. Melting Ice: When ice melts, it absorbs energy from the surroundings to break the bonds between water molecules, turning it into liquid water. This is why melting ice can cool down a drink.

Practical Applications

• Cold Packs: As mentioned before, cold packs used for injuries contain ammonium nitrate or other salts that absorb energy when they dissolve, providing a cooling effect.
• Refrigeration: Refrigerators work by using a refrigerant that absorbs heat from the inside of the refrigerator and releases it outside. The process of absorbing heat is endothermic.
• Air Conditioning: Similar to refrigerators, air conditioners use a refrigerant to absorb heat from the air inside a room and release it outside.

Key Words

• Endothermic reaction
• Energy absorption
• Enthalpy change
• Positive enthalpy change
• Heat absorption
• Temperature decrease

Conclusion

Understanding endothermic reactions is crucial for comprehending many everyday phenomena. By recognizing the key concepts and examples, you can better grasp the principles of energy transfer in chemical reactions.